The only region where diesel passenger cars sell in equal numbers to gasoline-powered vehicles is Europe.

And until the advent this year of tougher Euro 6 emission standards, new European diesel cars were significantly dirtier than those sold since 2008 in North America.

But one European transport analysis group suggests that the newest European “clean diesels” actually emit far higher levels of nitrous oxides (NOx) than the legally permitted limits.

A report issued last October by the International Council on Clean Transportation (ICCT) showed that real-world emissions were far higher than the new Euro 6 emission standards and the U.S. Tier 2, Bin 5 limits would allow.

As the ICCT wrote in a summary, “On average, real-world NOx emissions from the tested vehicles were about seven times higher than the limits set by the Euro 6 standard.”

It said the excess emissions “could not be attributed to ‘extreme’ or ‘untypical’ driving.”

“Instead,” it concluded, “they were due to transient increases in engine load typical of everyday driving (e.g., going up a slight incline), or to normal regeneration events in the normal diesel exhaust aftertreatment systems.”

Read more: Green Car Reports